The present invention is directed to an improved actuator for plug-type valves. The particular use made of the valve does not constitute a limitation of the present invention.
Prior art workers have utilized a number of arrangements of cam slots and cam follower means for translating linear motion into rotative motion, or vice versa, in association with the actuation of valves. Exemplary arrangements are taught in U.S. Pat. Nos. 2,703,589; 2,883,144; 3,078,065; 3,319,925; 3,370,827 and 3,450,382.
U.S. Pat. No. 3,184,214 teaches a cam operated actuator for a plug valve. The plug valve is provided with a tubular coupling member having cam slots formed therein. The cam slots, however, simply convert linear motion to rotative motion to rotate the plug between its open and closed positions. The arrangement does not vertically shift the valve plug.
Prior art workers having also developed actuators for valves of the plug type wherein when the plug is to be shifted from its valve-closed position to its valve-open position, it is first lifted vertically and thereafter rotated. When the valve plug is to be shifted from its valve-open position to its valve-closed position, it is first rotated and thereafter lowered to its valve-closed position. U.S. Pat. No. 2,596,075 teaches a special thread and dog arrangement for accomplishing such movement of the valve plug. U.S. Pat. No. 3,492,880 sets forth cam slot and cam follower means for accomplishing this motion of the valve plug. In both of the last mentioned patents, the vertical linear motion and the rotative motion are wholly separate, occurring one after the other. The structures of both of these patents are extremely complicated, requiring numerous parts.
The actuator of the present invention represents an improvement over actuators of the type taught in the last mentioned United States Letters Patent. When the actuator shifts the plug from its valve-closed position to its valve-open position, it first lifts the plug vertically without rotation and thereafter simultaneously lifts and rotates the valve to its final valve-open position. During the valve closing procedure, the actuator first simultaneously rotates and lowers the plug and thereafter continues to lower the plug without rotation into its final valve-closed and sealed position. As a result, the resilient seals of the plug are never rotated when in contact with the valve body, thus preventing abrasion of the resilient seals. The valve actuator comprises a minimum of parts, all of which are readily serviceable and replaceable. As a result, the actuator is extremely simple in construction and inexpensive to manufacture.
The actuator is self-locking against torque imparted to the plug by the fluid medium passing through the valve. Rotation of the plug 90.degree. between its valve-open and valve-closed positions is accomplished in a minimum of vertical travel of the plug and since this rotation is accomplished simultaneously with a portion of the vertical shifting of the plug during both the opening and closing operations, the actuator can be more compact than actuators heretofore developed.